Approaches to terpenoid natural products using reactive intermediates

Two attempted syntheses of a functionalized ring system common to kaurenoid natural products is presented. One of the attempts employed a bridgehead enone as a dienophile in a Diels-Alder reaction. One example in this series resulted in the synthesis of the tetracyclic ring system, but the angular C-8 (kaurene numbering) methyl group could not be added. Another example in this series resulted in the synthesis of a tricyclic intermediate containing the carbons to form the fourth ring, but this could not be cyclized. The other approach employed a Michael addition followed by an oxy-ene reaction for the synthesis of the tetracyclic framework, but a suitable precursor for the oxy-ene reaction was not realized. Also described is an attempted cyclization of a bicyclic intermediate to a tricyclic intermediate that contained functionality to prepare the bicyclo (3.2.1) octene ring system using a variety of reagents, but with no success;A synthesis of an advanced intermediate toward the synthesis of trixikingolide is also described. This synthesis employed bridgehead carbocation chemistry in the construction of a key intermediate. A tricyclic intermediate is prepared by a regioselective intramolecular aldol condensation. This intermediate contains the necessary functionality to synthesize the pentacyclic ring system common to this class of natural products